Changes in Network Structure of Chemical Gels Controlled by Solvent Quality through Photoinduced Radical Reshuffling Reactions of Trithiocarbonate Units.

Changes in the structure of networks of chemical gels cross-linked by covalent bonds have been investigated using reshuffling (i.e., degenerative exchange) reactions of the covalent bonds. These reactions can be applied to form functional materials including self-healing polymers, plasticity in cross-linked polymers, and shape-memory polymers. Herein, network structures of chemical gels were changed through radical reshuffling reactions of trithiocarbonate (TTC) units, and swelling degrees or network sizes were controlled by solvent quality. The chemical gels were prepared by RAFT copolymerizations of butyl acrylate and a TTC cross-linker, and the swelling degree was different for polymers prepared by solution or bulk polymerization. The cross-linked polymers were swollen in either good or nonsolvents and then exposed to UV light to trigger the radical reshuffling of the TTC units. The degree of swelling and network size in toluene increased in the presence of good solvents, whereas they decreased in nonsolvents. The repetitive changes in the degree of swelling were accomplished by changing the order of exposure to solvents.